Deal or no deal. The legal dynamics of Remaining.

How, after Article 50 is triggered, will the law shape and constrain our future inside and outside the EU?

To answer that question let me make some assumptions.

First, assume that Theresa May triggers Article 50 on 29 March 2017. And, second, assume that we can unilaterally revoke Article 50. (The Dublin case is progressing. Slowly but well. The Good Law Project will publish an update next week here. Please sign up to our mailing list).

What happens next? Is there a legal path to Remaining? How will this shape and be shaped by the politics?

There are three main scenarios going forward. They involve a delicate and complex interplay of EU and UK law. I'll set them out and then - once I've run through the analysis - address what seem to me to be the main points of interest.

(1) We conclude an agreement with the EU which Parliament approves. We then leave the EU on the date - it may be less or it may be more than two years from 29 March 2017 - set out in that agreement. The precise date of our departure depends on what the agreement provides: Article 50(3) says that the Treaties cease to apply to us "from the date of entry into force of the withdrawal agreement."

(2) We don't conclude a deal with the EU. The key fact to bear in mind is this: as a matter of EU law we remain in the EU until 29 March 2019 and we then we leave. But as a matter of UK law, whether we leave before 29 March 2019 depends upon the status of the European Communities Act 1972 (the "ECA").

Theresa May will ask Parliament (in her so-called Great Repeal Bill) to give her power to repeal the ECA at a moment of her choosing. If you assume Parliament has not given her that power then it would be for Parliament to choose - in response to talks with the EU breaking down - whether to repeal the ECA or to take some other action. It is difficult (for me) to imagine that Parliament might ask the PM to recommence negotiations. But it could very well put back to the electorate the choice whether to leave the EU without a deal or to Remain. And if a Referendum produced a Remain result before 29 March 2019 we would Remain in the EU as a matter of both UK and EU law.

If, on the other hand, Parliament had given her that power then you would expect Theresa May to repeal the Act when talks with the EU break down. That would have the consequence that we would be out of the EU as a matter of UK law. But, until 29 March 2019, we would still be in the EU as a matter of EU law. Parliament could still in theory - I will return to consider the practice below - call a referendum on whether to leave the EU or to Remain. And if that Referendum produced a Remain result before 29 March 2019 Parliament could re-enact the ECA and we would Remain in the EU as a matter of both UK and EU law.

(A small aside. I don't understand why Parliament should prospectively repeal the ECA. To do so is unnecessarily to abrogate a power that properly belongs to Parliament. But perhaps in the final analysis it doesn't matter hugely).

(3) We conclude a deal with the EU and Parliament doesn't approve that deal. This scenario may be less likely than (1) or (2) but its effects are substantially identical to scenario (2). (It is possible that our membership of the EU would, as a matter of EU law, expire on the date prescribed by the rejected agreement (see Article 50(3)). But I think the better view is that the withdrawal agreement would never "enter into force".) So, until 29 March 2019, Parliament could choose to Remain.

So a few points emerge from this analysis and generally.

(i) Parliament still has a lot of power. Whatever the Prime Minister does, Parliament can still decide to Remain in the EU.

(ii) opinions differ but my own view is that party politics is not the insuperable barrier to Remaining that many think. This is not the place for a lengthy analysis of the point but I proceed from the premise that Labour MPs are basically Remain and there is a substantial body of Conservative MPs who are basically pragmatic. This, of course, is not to deny that the political situation could be better for those like me who still think the country's interests are better served by us Remaining.

(iii) if you believe that leaving the EU is a bad thing, and that the public will come to appreciate this, then scenario (2) is rather striking. If negotiations with the EU deteriorate and break down we will see how the economy reacts. And we will also see the - hitherto under-examined - other non-financial consequences: for Scotland, for Northern Ireland, for the right of UK citizens living in the EU and EU citizens living here to reside and access healthcare, for air transportation and the NHS and so on. And we will see how the public reacts to this. Scenario (2) could very well confront the electorate with a stark choice between the having and the eating of cake. And at a point in time when Parliament can still react to the electorate's choice.

This is a reality which could shape both the EU's and our own conduct of negotiations.

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